1. Field of the Invention
The present invention relates to a liquid droplet discharge head and a liquid droplet discharge device, and more particularly, to a liquid droplet discharge head and a liquid droplet discharge device which applies liquid droplets onto an object by discharging liquid from nozzles.
2. Description of the Related Art
A known example of a liquid droplet discharge head and a liquid droplet discharge device using same is an inkjet printer equipped with a recording head formed with a plurality of nozzles which discharge ink.
An inkjet printer discharges ink from nozzles of pressure chambers by means of the pressure generated when the pressure chambers of the recording head are deformed mechanically, or when air bubbles are formed by switching on a heater disposed in the ink flow channel, the discharged ink being applied to an object (recording medium), such as recording paper. The recording head and the recording medium are moved relatively to each other, thereby forming a desired image on the recording medium. Therefore, the quality of the image formed is largely dependent on the performance of the recording head provided in the printer.
However, air bubbles may become trapped inside the recording head when ink is first filled into the head, and air bubbles may also enter into the ink flow channels via the nozzles, due to the pulsating action generated in the ink. Air bubbles of this kind impede the supply of ink and absorb the pressure created in order to discharge the ink, and consequently, they may lead to ink discharge errors in the nozzles, such as defects in the ink discharge volume (the dot size ejected onto the recording medium), the flight direction (droplet ejection position), the flight velocity (droplet ejection position), and the like. Such errors can cause the quality of the recorded image to decline.
In order to resolve these problems, there are commonly known technologies which expel air bubbles by performing restoring processes (flushing, wiping, preliminary discharge, nozzle suction, and the like) in the recording head as and when necessary. Furthermore, inventions have been disclosed which seek to improve air bubble expulsion characteristics, and to improve the stability of ink discharge from the nozzles during image formation (see Japanese Patent Application Publication Nos. 9-226142, 2002-283585, 2002-361867 and 8-132640).
Japanese Patent Application Publication No. 9-226142, for example, discloses that ink flow speed in the ink supply section is accelerated and air bubble expulsion properties are improved by making the cross-sectional area of the ink supply section to the pressure chambers smaller than the cross-sectional area of the common liquid chamber (which is provided on the upstream side of the pressure chambers).
Japanese Patent Application Publication No. 2002-283585 discloses an ink supply shape for a matrix type recording head having good stability at high speed, and it also states that the stability of continuous, high-speed ink discharge is improved by setting numerical limits on the flow channel resistance of the ink supply section.
In Japanese Patent Application Publication No. 2002-361867, ink supply ports (the liquid supply devices described in Japanese Patent Application Publication No. 2002-361867) are provided in the center and at either end of the main flow path of a matrix-type recording head, whereby the flow channel resistance is reduced and the recording head is made more compact in size.
Japanese Patent Application Publication No. 8-132640 discloses improvement in the stability of continuous, high-speed ink discharge by seeking to reduce the pulsating action of a pump by adopting a circulatory ink supply by means of buffer tanks.
Furthermore, Japanese Patent Application Publication No. 9-286098 discloses a line type head having ink supply ports provided at either end of the lengthwise direction of a recording head.
Japanese Patent Application Publication Nos. 9-226142 and 2002-283585 disclose technology for improving the expulsion of air bubbles during nozzle suctioning, by increasing the flow speed in the ink supply channel and providing dummy nozzles. However, since the ink supply channel has end sections, air bubbles are liable to collect in these end sections and hence there is a problem in that air bubbles are not expelled satisfactorily. In nozzle suction performed in order to expel air bubbles trapped in end sections such as these, it is necessary to suction a large amount of ink. In particular, when technology of this kind is used in a long recording head, it is necessary to suction an even greater quantity of ink.
Japanese Patent Application Publication No. 2002-361867 discloses technology which reduces the flow channel resistance by providing ink supply ports in the center or the respective ends of the main flow path, but since only one or two ink supply ports are provided, a problem arises in that ink supply deficiencies become more liable to occur, the larger the size of the recording head, for instance, in a line type inkjet head. Furthermore, since the ink supply channel has end sections, similarly to the prior art, air bubbles are not expelled in a satisfactory manner.
In the technology described in Japanese Patent Application Publication No. 8-132640, various ink supply modes are disclosed in a line type recording head, such as a sub-tank refill mode, discharge refill mode, discharge restoration mode, pressurized discharge restoration mode, and the like. However, there is no description regarding the structure of the internal flow channels of the head and neither is there any description regarding application to a matrix type recording head.
Japanese Patent Application Publication No. 9-286098 discloses a recording head having ink supply ports in the respective end sections of the recording head in the lengthwise direction thereof, but it does not provide a specific description of the ink supply. Furthermore, in a recording head of this kind, it is difficult to achieve stable ink supply in a large matrix type recording head of long dimensions.